Opthalmic lenses having reduced base out prism

ABSTRACT

The invention generally relates to a lens and the method of manufacturing progressive addition lenses (PAL) to remove unwanted base out prism and minimize excessive convergence, comprising determining basic configuration of two major lens surfaces to provide a distance portion and near portion, wherein diopter power increases from the distance portion of the lens to the near portion; selecting an amount of prism reduction; and reducing base out prism that inherently occurs as diopter power increases by altering the configuration of the lens as a function of the amount of prism reduction to minimize any disruption of optical properties a lens while decreasing base out prism.

CROSS REFERENCE TO RELATED APPLICATIONS

There are no related applications.

FIELD OF THE INVENTION

This invention relates to ophthalmic lenses. In particular thisinvention is directed to reducing unwanted base out prism by changingthe lens surface to cause minimal disruption to other optical propertiesof the lens.

BACKGROUND OF THE INVENTION

With normal vision, an individual is able to change focus for differentdistances. Ideally, an individual is able to focus on distant objects,referred to as distance vision, and on near objects, referred to as nearvision. The optical system of the eye uses numerous muscles to focus forboth distance and near vision. These muscles allow the eye to adjustfocus when transitioning between distance vision and near vision. Thereare various responses involved in changing focus from distance vision tonear vision. These include making the image clearer, the eyes turning inor out, and pupils changing size. If the eyes do not turn in enough withnear vision, for example, then the individual would see double.

Single vision lenses have been used for many years to correctfarsightedness, nearsightedness, and astigmatism (ametropia). When welook directly through the optical center of a single vision lens thereis no prismatic effect induced in any direction. As your eyes move awayfrom the optical center of a lens (correcting ametropia) prism resultsand increases as you move farther from the optical center. This prism ismostly induced by the curvature difference in the two major lenssurfaces and is the result of moving away from the optical center. Theamount of prism changes with both power and distance from the opticalcenter. The stronger the lens and the farther from the optical centerthe more prism is induced. For someone that is farsighted wearing a lensto correct hyperopia, converging to a near object causes the eyes tolook towards the nasal side of the optical center of the lenses. In thisinstance base out prism would be induced when looking at near thereforecausing an increase in the convergence demand necessary to view theobject under binocular conditions. This increased convergence can be asource of asthenopia.

Bifocals, including progressive addition lenses (PALs), have been usedfor many years to help with presbyopia. PALs provide the ability for aperson wearing these type of lenses to see at different distances. PALsor Bifocals are generally needed when the eye can no longer make thetotal change in focus necessary from distance to near. PALs typicallyprovide a distance portion in the lens (this would include the patient'sprescription to see clearly at a distance) and a smooth graduatingcontinuous change in dioptric power to a near power (this would be thediopter add power for the patient to see clearly at near). PALs have nolines or edges visible between changes in dioptric power. PALs areavailable for example in different add powers, corridor lengths andcorridor widths depending on the need.

Prior art PALs thus traditionally include undesired base out prism thatis induced at near when the optical surface of the lens is altered tocreate the add power at near.

SUMMARY OF THE INVENTION

This invention relates to reducing unwanted base out prism by changing alens to cause minimal disruption to other optical properties of thelens. There is disclosed in accordance with one aspect of the inventionan improvement in a progressive addition lens (PAL) comprising adistance portion and a near portion, wherein dioptric power increasesfrom the distance portion of the lens to the near portion. Theimprovement consists of a lens being formed to reduce base out prismthat inherently occurs as the add power increases. The lens is alteredto minimize any disruption of optical properties of the lens whiledecreasing the base out prism.

It is a feature of the invention that the lens comprises two majorsurfaces, each major surface being defined by a set of Cartesiancoordinate points. The points are selected to alter the prism propertiesof selected zones of the lens.

It is another feature that at least one of the major surfaces is alteredto modify tilt applied to the one major surface at each point byapplying a weighting factor. The weighting factor may gradually increasetraversing from the distance portion to the near portion. Also, theweighting factor may gradually increase and then decrease traversingfrom one side of the lens to the other. The weighting factor may varybetween 0 and 1. The weighting factor may vary according to a selectdesired prism change to be added to the undesired base output prism.

There is disclosed in accordance with another aspect of the invention animprovement in an ophthalmic lens consisting of a lens being formed toreduce increasing base out prism that inherently occurs when the eyesare viewing an object under binocular conditions away from an opticalcenter of the lens. The lens is altered to minimize any disruption ofoptical properties of the lens while decreasing base out prism.

There is disclosed in accordance with another aspect of the inventionthe method of manufacturing progressive addition lenses (PAL) to removeunwanted base out prism which minimizes excessive convergence neededwhen viewing objects within the intermediate and reading portions of thelens, comprising the steps of: determining the basic configuration oftwo major lens surfaces to provide a distance portion and near portion,wherein dioptric power increases from the distance portion of the lensto the near portion; selecting an amount of prism reduction; andreducing base out prism that inherently occurs as diopter powerincreases by altering the configuration of at least one of the majorlens surfaces as a function of the amount of prism reduction to minimizeany disruption of optical properties of a lens while decreasing base outprism.

Further features and advantages of the invention will be readilyapparent from the specification and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, front elevation view of eyeglasses including amultifocal ophthalmic lens in the form of a progressive addition lens inaccordance with the invention;

FIG. 2 is a curve illustrating a weighting factor applied to a tiltangle relative to a Y axis for the lens of FIG. 1;

FIG. 3 is a curve illustrating a weighting factor applied to a tiltangle relative to an X axis for the lens of FIG. 1;

FIG. 4 is a diagram of a lens showing areas of relative reduced base outprism in accordance with the invention; and

FIG. 5 illustrates a lens and cross sections showing modification in thesurface of the lens of FIG. 1 in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to single vision, and multifocal ophthalmiclenses. In particular this invention is directed to progressive additionlenses (PALs) in which under the current art base out (Bo) prism isgenerally increasing from the distance portion of the lens to the nearportion of the lens, this not accounting for the patients ametropia. Itis common that negligible or no base out prism is induced at the opticalcenter/prism reference point, and as much as one diopter of unwantedbase out prism is present at the reading or near portion of the lens.This occurs as changes take place to produce the reading addition power.This invention reduces this unwanted base out prism by changing themajor lens surfaces, either on the front surface, back surface, orinternally within the lens, in such a way as to cause minimal disruptionto other important optical properties of the lens.

A progressive addition lens is one lens that has at least oneprogressive addition surface which could be placed on either or bothsides of the lens or within the lens itself. Referring to FIG. 1, aprogressive additional lens 10 is illustrated in a frame 12. The lens 10is illustrated with dashed lines to separate different portions of thelens 10. Particularly, a distance portion 14 is separated from a nearportion 16 by an intermediate portion 18. The different portions aredefined by a progressive surface which is an aspheric surface in whichthe distance portion 14 and near portion 16 are connected by a smoothand continuous changing increasing dioptric power in the intermediateportion 18 from the distance portion 14 to the near portion 16. Adistance vision correction amount, expressed in diopters, is used in thedistance portion 14. “Add power” is the amount of dioptric powerdifference added to the distance correction in the near portion 16.

The present invention reduces unwanted induced prism commonly found insingle vision lenses and progressive multifocal lenses (PALs) andtraditional bifocal lens when the eyes are viewing object underbinocular conditions away from the optical center of the lens. When anindividual changes gaze from a distance object to near object the eyesconverge to the point being viewed. Some lenses and particularlyprogressive lenses exhibit base out prism as the patients' eyes begin tolook at the object away from the optical center of the lens. Previousmultifocal and single vision lenses have not addressed the change inconvergence necessary to maintain binocularity that occurs when the eyestranslate into a portion of a single vision lens away from the opticalcenter and into the reading area of a multifocal lens. In particular ifthe patient's correction is negated with the current art of makingprogressive multifocal lens base out prism is increasing from thedistance portion of the lens to the reading portion of the lens. Thisbase out prism requires additional convergence of the human eyes inorder to maintain convergence on the object in which they are viewing.This increase in convergence can create asthenopia for the individual.

This invention of ophthalmic lenses defines a lens design and method forremoving the unwanted base out prism which increases the convergencedemand on the visual system when viewing an object at near (whichgenerally is away from the distance optical center of the lens). Thisreduction in base out prism allows the viewer to have reduced need toconverge when looking through the portion of the lens that is outsidethe optical center. In particular this invention helps reduce theunwanted base out prism when viewing object through the add portion of aPAL lens. Traditionally, prism is placed into the entire lens thereforenot varying the amount of prismatic effect as the eye is moving awayfrom the optical center of the lens. Also traditionally increasing ordecreasing amounts of prism are not intentionally induced in the lens toadd to or take out the prism that is induced because of the lens design.

It is the discovery of this invention that the continuous change in addpower of progressive addition lenses (PAL) from the distance zone to thenear zone while controlling any unwanted base out prism reduces the needfor the eyes to converge more than normal at near. This thereforereduces eye strain. The lens is altered in such a way to reduce thehorizontal base out prismatic effect and causing minimal disruption toother important optical properties of the lens. This reduction of baseout prism is not a by-product of the resultant nature of progressivelenses but a desired outcome and design of the lens.

It is also a discovery of this invention that when a single visionlenses is used to correct ametropia that prism is induced when lookingaway from the optical center of the lens. This prism will vary dependingupon the power of the correction and the distance from the opticalcenter. Reduction of this induced prism can be counteracted by alteringthe lens in order to reduce any unwanted change in prism when lookingaway from the optical center. The amount of prism induced will beincreased as the resultant nature of the prism increases the further youget from the optical center of the lens.

One method in accordance with the invention comprises manufacturingprogressive addition lenses (PALs) to remove unwanted base out prism andminimize excessive convergence. This comprises: determining the basicconfiguration of the two major lens surfaces to provide a distanceportion and near portion, wherein dioptric power increases from thedistance portion of the lens to the near portion; selecting an amount ofprism reduction; and reducing base out prism that inherently occurs asdioptric power increases by altering the configuration of at least oneof the major lens surfaces as a function of the amount of prismreduction to minimize any disruption of optical properties a lens whiledecreasing base out prism. Each major surface is defined by a set ofx,y,z Cartesian coordinate points, as is known. In accordance with theinvention, the points are selected to alter the prism properties ofselected zones of the lens.

One exemplary method of achieving this result is to apply a functionz=F(x, y) at each point. This function modifies the tilt applied to thesurface to achieve the desired prism by applying two weighting functionsand F_(x) and F_(y). The weighting functions modify the angle of tilt ina controlled manner in order to disturb the surface as little aspossible and keep unwanted distortion to a minimum. These functionsF_(x) and F_(y) both vary between 0 and 1 and modify the angle of tiltby simple multiplication. The function F(x, y) would be applied at thepoint (x_(i), y_(i)) as follows:F(x _(i) ,y _(i))=z _(i) +x _(i) tan(θ×F _(y) ×F _(x))

where z_(i) is the original height of the point at (x_(i), y_(i)) andF(x_(i), y_(i)) is the modified height to give the desired prism.

The angle of tilt θ required to give the desired prism is given by

$\theta = \frac{\tan^{- 1}\lbrack \frac{P}{100} \rbrack}{( {n - 1} )}$

-   -   where: P=desired prism change to be applied in prism dioptres. P        can be selected based on design considerations and patient        trials. n=refractive index of lens material and F_(x) and F_(y)        are two weighting functions used to modify the angle of tilt by        simple multiplication and are determined as follows:        F_(y) is given by:

$\begin{matrix}{y_{i} > y_{start}} & {F_{y} = 0} \\{y_{start} \geq y_{i} \geq {y_{end}\text{:}}} & {F_{y} = {0.5\{ {{\cos\lbrack \frac{( {y_{i} - y_{end}} )\pi}{( {y_{end} - y_{start}} )} \rbrack} + 1} \}}} \\{y_{i} < {y_{end}\text{:}}} & {F_{y} = 1}\end{matrix}$FIG. 2 shows how this weighting function F_(y) changes from the top ofthe lens to the bottom of the lens.F_(x) is given by:

$\begin{matrix}{x_{i} < {{- x_{b}}\text{:}}} & {F_{x} = 0} \\{{- x_{b}} \leq x_{i} \leq {{- x_{a}}\text{:}}} & {F_{x} = {0.5\{ {{\cos\lbrack \frac{( {x_{i} + x_{a}} )\pi}{( {x_{b} - x_{a}} )} \rbrack} + 1} \}}} \\{{- x_{a}} \leq x_{i} \leq {x_{a}\text{:}}} & {F_{x} = 1} \\{x_{a} \leq x_{i} \leq {x_{b}\text{:}}} & {F_{x} = {0.5\{ {{\cos\lbrack \frac{( {x_{i} - x_{a}} )\pi}{( {x_{b} - x_{a}} )} \rbrack} + 1} \}}} \\{x_{i} > {x_{b}\text{:}}} & {F_{x} = 0}\end{matrix}$

FIG. 3 shows how this weighting function F_(x) changes from one side ofthe lens to the other side of the lens.

FIG. 4 shows the co-ordinate system used relative to a lens inaccordance with the invention. The y axis is vertical (top to bottom onthe lens) and the x axis is horizontal (side to side on the lens). The zaxis (not shown in the drawing) is perpendicular to the plane formed bythe x and y axes. FIG. 4 also shows exemplary areas on the lens surfacewhich are affected by F_(x) and F_(y). The intersection of the x and yaxes is the optical center of the lens. In this illustration, no prismis added in most of the upper portion of the lens. Particularly, noprism is added in the area above the line labeled y_(start) or outsidethe areas bounded by lines −x_(b) to x_(b). Otherwise, the illustrationsshow six generally rectangular areas. As will be apparent, the areas onthe lens are not rectangular, but this is used to divide the lens intoareas for general characterization purposes herein. Area 2 whichincludes the optical center has constant prism added in a horizontaldirection the value of which increases vertically from top to bottom.Area 5 has the full amount of prism added. Areas 1, 3, 4 and 6 have theamount of added prism reduced going toward the edges from the y axis.This should be apparent by considering the weighting factor graphs ofFIGS. 2 and 3 relative to the corresponding points on the diagram movingvertically on the y axis or horizontally on the x axis.

FIG. 5 shows the physical effects (exaggerated) on the lens surface atfour different positions. Particularly, the cross section for y_(start)illustrates that no changes have been made, while traversing through thesubsequently lower cross section tilt angles are altered to reduceincreasing base out prism while minimizing any disruption of opticalproperties. As will be apparent, on the actual lens surfaces, thesurface modifications area done gradually and the illustrationexaggerates the effect for purposes of illustration and understanding.

The y_(start) and y_(end) positions correspond with those shown in FIGS.2 and 4. y₁ and y₂ are two intermediate positions. At the y_(start)position the original surface has not been affected. y₁ and y₂ positionsshow the prism effect increasing in accordance with F_(y). At they_(end) position the maximum prism effect of F_(x) and F_(y) has beenachieved. In this example, this prism effect is then maintained at thisconstant value to the bottom of the lens.

−x_(b), −x_(a), x_(a) and x_(b) also correspond with those shown inFIGS. 3 and 4. In this example the nasal side of the lens is on theright and it can be seen that constant Base-in prism has been achievedbetween −x_(a) and x_(a). Between −x_(b) and −x_(a), and between x_(a)and x_(b) smooth blending of the surface is achieved in accordance withF_(x).

As is known, when an individual looks from the distance portion of thelens to the near portion the eye does not transcend vertically but at anangle down and in. This is referred to as the eye path or corridor path.A progressive addition lens is typically fitted at distance a fewmillimeters above the prism reference point of the lens. The connectingline between this point and the near reference point would be consideredto be the eye path or the corridor path. While this applicationdiscusses reduction of base out prism relative to an axis transcendingvertically and what happens to the lens in a horizontal and verticaldimension, the correction may in fact be applied relative to thecorridor path, as will be apparent to one skilled in the art.

The lenses in accordance with the invention may be fabricated by anyconventional methods and all known materials suitable for production ofophthalmic lenses. Such materials can include all glass, polycarbonate,polymethylmethacrylate, and other high index materials. Further, thelenses may be produced by any suitable techniques including but notlimited to grinding, casting, laminating, surface casting,thermoforming, or a combination thereof.

While the present invention is specifically described with respect to amultifocal ocular lens in the form of progressive addition lenses, theconcepts of the invention can be applied to non-progressive lenses, suchas bifocals or trifocals, or to single vision lenses.

Thus, in accordance with the invention, there is provided a multifocalocular lens in which inherent base out prism due to the increase inpower between the distance and near portions is removed.

1. In a progressive addition lens (PAL) comprising a distance portionand near portion, wherein diopter power increases from the distanceportion of the lens to the near portion, the improvement consisting ofthe lens being formed to reduce base out prism that inherently occurs asthe add power increases, the lens being altered to minimize anydisruption of optical properties of the lens while decreasing the baseout prism.
 2. The improvement of claim 1 wherein the lens comprises twomajor surfaces, each major surface being defined by a set of Cartesiancoordinate points, the points being selected to alter the prismproperties of selected zones of the lens.
 3. The improvement of claim 2wherein tilt applied at each point to at least one of the major surfacesis modified by applying a weighting factor.
 4. The improvement of claim3 wherein the weighting factor gradually increases traversing from thedistance portion to the near portion.
 5. The improvement of claim 3wherein the weighting factor gradually increases to a maximum value of 1and then decreases as the lens is traversed from one side of the lens tothe other in the x direction over a predetermined area in the ydirection.
 6. The improvement of claim 3 wherein the weighting factorvaries between 0 and
 1. 7. The improvement of claim 3 wherein theweighting factor varies according to a select desired prism change to beadded to undesired base out prism.
 8. A method of manufacturing aprogressive addition lens. (PAL) to remove unwanted base out prism andminimize excessive convergence, comprising the steps of: determiningbasic configuration of two major lens surfaces to provide a distanceportion and near portion, wherein diopter power increases from thedistance portion of the lens to the near portion; selecting an amount ofprism reduction; and reducing base out prism that inherently occurs asdiopter power increases by altering configuration of at least one of themajor lens surfaces as a function of the amount of prism reduction tominimize any disruption of optical properties of the lens whiledecreasing base out prism.
 9. The method of claim 8 wherein each majorsurface is defined by a set of x,y,z Cartesian coordinate points and thepoints are selected to alter the prism properties of selected zones ofthe lens.
 10. The method of claim 9 wherein tilt applied at each pointto at least one of the major surfaces is modified by applying aweighting factor.
 11. The method of claim 10 wherein the weightingfactor gradually increases to a maximum value of 1 and then decreases asthe lens is traversed from one side of the lens to the other in the xdirection over a predetermined area in the y direction.
 12. The methodof claim 10 wherein the weighting factor gradually decreases traversingfrom a corridor path of the lens to sides of the lens.
 13. Eyeglassescomprising: a frame; and a progressive addition lens (PAL) in the framecomprising a distance portion and near portion, wherein diopter powerincreases from the distance portion of the lens to the near portion, thelens being formed to reduce increasing base out prism that inherentlyoccurs as the add power increases, the lens being altered to minimizeany disruption of optical properties of the lens while decreasing thebase out prism.